9. No, (-2,3) is not the solution of the system as it doesn't satisfy the 2nd equation (x= y-4) substituting the value of x=-2 and y=3 we will get, -2 = 3-4, that is -2=-1 which is not true.

10. Yes, (-2,3) is a solution of the given system, since it satisfies both the equations. substituting value of x=-2 and y=3 we will get, -2+3=1, that is 1=1, which is true